CHEM 2211 1nd Edition Lecture 2 Outline of Last Lecture I Rules and principles II Bonding III Structures Outline of Current Lecture II Polar bonds vs molecules III Perspective diagrams and structures Current Lecture II Polar bonds vs polar molecules Polar bond A bond in which an electron is shared unequally resulting in partial positive and negative charges A molecule that is comprised of polar bonds can be a polar molecule or a non polar molecule depending on its symmetry Polar molecule A molecule that is not perfectly symmetrical so the charges do not cancel out Such as o H H pt Cl Cl o Say all the bonds here are polar The molecule is only polar if the bonds do not cancel out this can be shown with arrows These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute The polar bonds between the center molecule and the H atoms would have arrows going from H to the center Whereas the polar bonds between the center molecule and the Cl atoms would have arrows going from the center molecule to the Cl atoms o H H pt Cl Cl The direction of the arrow specifies where the partial charges go The head of the arrow points to the atom that will hold on to the electron more o The partial negative atom The base of the arrow is the atom that will be lacking the electron most of the time o The partial positive atom The diagram shows us that the electrons are not evenly distributed resulting in the polar charge of this molecule Non Polar molecule A molecule that is perfectly symmetrical Such as o Cl Cl pt Cl Cl o This molecule is perfectly symmetrical o The electron in each polar bond on every side of the molecule are shared the same o This results in a non polar molecule even though it is made up of polar bonds III Perspective diagrams and structure Perspective diagram Shows how each atom is bonded to the center atom its stereochemistry or orientation in space When drawing one of these diagrams there are 3 elements 1 lines 2 dashed wedges I will use to represent dashed wedges 3 Wedges Lines show that the atom is in the same plane as the one it is connected to Dashed wedges show the that the atom is away from you behind the atom it is connected to Wedges show that the atom is coming out at you in front of the atom it is connected to Ex Cl H C H H Structures The most common structure to be used in organic chemistry is skeletal structure Skeletal structure Omits hydrogens Uses end points as carbons Writes in any atom that is not carbon at endpoints where it exsist Looks like zig zags is the easiest way to remember this structure These simple lines represent the formula C5H12 C Ex C C The point where to lines meet like above represent the C atoms Carbons are also present at the end of each line as above You get the hydrogen number by forfilling the octet rule o An atom is full when it has 8 electrons surrounding it o Every bond is 2 So a middle carbon at the meeting of two lines has 4 electrons o 2 from each bond to the surrounding carbons o It is also bonded to unwritten hydrogens o If it has two bonds already it is bonded with two hydrogen as well If its an end carbon o It is only bonded to one carbon you can see o Then it needs three more bonds with unwritten hydrogens You add up all the unwritten hydrogens to get the H12 If we wanted to have C3H7NH3 in skeletal structure we would draw N Any atom that is not carbon or hydrogen must be specifically written in in its place
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